This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. Hei. 7-327605 filed on Dec. 15, 1996, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present application relates to a driving apparatus for a vehicle, and more particularly to a driving apparatus capable of driving four wheels of an electric vehicle.
2. Related Arts
When four-wheel driving is attempted to be done in an electric vehicle, it is conceivable that an electric motor is used in substitution for a conventional internal combustion engine. However, in this case, mechanical loss of driving power is large due to a driving power transmission mechanism such as a center differential gear. As a result, loads on the electric motor and a battery become heavy.
To solve this problem, Japanese Patent Laid-Open Publication No. Hei. 2-133006 teaches a driving apparatus in which electric motors are provided on each of four wheels and thereby enable the four wheels to be driven separately.
According to the driving apparatus described above, since each of the four wheels is separately and directly driven by a respective electrical motor, mechanical loss of driving power can be made smaller. However, if a noise signal enters wires connected to the electric motors, driving torques of left and right wheels may lose their balance so that the electric vehicle can not run stably.
In view of the above problem, the object of the present invention is to provide a driving apparatus for a four-wheel drive vehicle in which a load on an electric motor is lightened by reducing mechanical loss due to a driving power transmission mechanism while maintaining a running stability of the vehicle.
According to the present invention, first and second dynamo-electrical machines are provided in a vehicle. A first rotor forming a part of the first dynamo-electrical machine together with a second rotor is connected to either one of a front driving shaft and rear driving shaft. The second rotor forming a part of the second dynamo-electrical machine together with a stator is connected to another one of the front driving shaft and rear driving shaft.
As a result, a torque generated by the first dynamo-electric machine is transmitted to a driving shaft connected to the first rotor. A torque which is the difference between a reaction torque caused by the torque generated by the first dynamo-electric machine and a torque generated by the second dynamo-electric machine is transmitted to a driving shaft connected to the second rotor. As a result, torques described above are distributed to front wheels and rear wheels.
According to the above-described structure, since a center differential gear is not needed to distribute driving torque, mechanical loss of driving torque can be made small. As a result, loads of the first and second dynamo-electric machines are lightened. Accordingly, since it is not necessary to enhance the performances of the first and second dynamo-electric machines, the size of each of the dynamo-electric machines can be made small. In addition, at least one of the front driving shaft and rear driving shaft is rotated by the first or second dynamo-electric machine. As a result, since left and right front wheels or left and right rear wheels are simultaneously driven at all times, stable running performance of the vehicle can be obtained.
The front driving shaft can be coupled to left and right front wheels via a differential gear. Also, the rear driving shaft can be coupled to left and right rear wheels via a differential gear. As a result, when the vehicle makes a turn, stable running performance of the vehicle can be obtained.
It is preferable that the first rotor and second rotor are connected to the front driving shaft and rear driving shaft, respectively. As a result, since the rear wheels have priority of driving over the front wheels, the vehicle can run more stably.